In light of the recent relationship between the ras genes and cyclic AMP synthesis in yeast, we have systematically characterized alterations in adenylate cyclase activity of NIH 3T3 cells transformed by ras genes. We have found that ras transformation produces an alteration in the ability of adenylate cyclase to respond to prostaglandin E1. We have been unable to detect any other changes in the activity of the adenylate cyclase system caused by overproduction of normal ras or mutant ras gene products. These findings suggest the G protein encoded for by ras is not itself a component of the adenylate cyclase system in NIH 3T3 cells.